The yeast Kluyveromyces lactis makes an inducible beta-galactosidase. The aim of the proposed research is to determine the molecular mechanism by which lactose induces beta-galactosidase. For several reasons this should be a good eucaryotic system for studying genetic regulation: Like the lac system of E. coli, the one in K. lactis makes a stable beta-galactosidase that is easy to assay and to purify since it is not part of an enzyme complex. Most likely the system involves only a few genes and induction is not sensitive to catabolite or nitrogen repression as are more complex systems in yeast. RNA-DNA hybridization techniques will be used to determine if mRNA for beta-galactosidase is synthesized de novo after induction. Likewise, experiments to examine whether the enzyme is synthesized de novo after induction are presented. Lactose minus mutants (lac minus) will be tested for complementation and recessiveness, and mapped by standard genetic techniques. They will be characterized by biochemical techniques in order to determine their molecular defect. The presence of a permease specific for lactose will be examined by standard procedures. Regulatory mutants such as those allowing constitutive synthesis of beta-galactosidase will be screened for and, if found, tested for dominance or recessiveness, mapped and examined biochemically. Procedures for trying to isolate a phage or plasmid carrying the gene (genes) for the beta-galactosidase of K. lactis are presented. The mechanism for regulating this gene will be examined in vitro using purified cell components.